Comparision the effects of wheat straw on physical and hydraulic properties of two fine and coarse - textured soils selected from semiarid region

: Soil physical quality of arid and semiarid regions is poor.The objectives of this study were to investigate the effects of wheat straw on some physical and hydraulic properties of two fine and coarse- textured solis selected from semiarid region. Soil samples were taken from Moghan plain . The study was conducted using PVC columns (20 cm diameter and 25 cm height).The straw rates were: o(control), 1, 2, 3,4 and 5 mass precent in the air – dried soil. The design of experiment was factorial with randomized block (factor A: used straw rates at 5 levels; factor B: soil textural class at 2 levels). The soil columns were incubated in greenhouse conditions (temprature of 22 ±4 ℃ and 0.5 to 0.75 FC soil moisture) for 6 months. Organic carbon (OC), particle density (Dp), mean weight diameter of aggregates (MWD), and residule soil moisture at 3000, 5000,10000 and 15000 cm were measured in disturbed soil samples using pressure plate instruwent. The bulk density (Db), saturated hydraulic conductivity (Ks), SMC at 0, 10, 20, 40, 60, 80, 100, 300, 600 and 1000 cm suctionc were determined in undisturbed soil samples using steel cylenders (5 cm diameter and 5cm height). The van Genuchten α and n parameter calculated using RETC software.from SMC data. The soil physical quality index (sp) computed by using saturated (θs), and resiual (θr) water contents, and VG-n parameters. The results showed that application of straw at the rates of 1 to 5% increased OC (4.4 to 47% and 15.1 to 105.6%), total porosity (10.5 to 42.1% and 31.4 to 65%), MWD (100 to266.2% to 2.5 to 62.5%), Ks ( 22 to 195.4 % and 80 to 162.85%),θFc (11.65 to 24.6% to 7.87 to 20%), θAW (20 to 26.6% and 12.5 to 59.37%),θr (33.3 to 66.3% and 9.1 to 54%), α (10 to 50% and 12/5 to 59.37%), VG- n ( 0.63 to 7% and 12.5 to 59.37%), and Sp (5.71 to 14.6% and 8.53 to 29.3%) and decreased Db ( 1.3 to 1.48% and 1.3 to 1.4%) compared with control in sandy loam and clay lome soils, respectively All used rates of straw significanty decreased macropores (>75 µm) in both soils celective to the control. Also microporres (<30 µm) in clay loam soil were significantly more than sandy loam soil. Therefore, application of wheat straw improved physical quality of the examined fine and coarse- textured soils. Although the improvement effects of straw on clay loam soil was more than sandy loam soil.